JP2006059704A - Negative electrode for lithium-ion secondary battery, and lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode for a lithium ion secondary battery in which, compared with a negative electrode consisting of conventional carbon material containing graphite or metal, there are no pulverization and separation of the active material, thereby discharge capacity is large and excellent cycle characteristics and initial charge and discharge efficiency can be obtained, and the lithium ion secondary battery using this secondary battery negative electrode and demonstrating the above characteristics. <P>SOLUTION: This is the negative electrode for the lithium ion secondary battery which has a metal-contained layer that contains a carbon material and a metal capable of alloying with lithium of 1-100 parts by mass against the carbon material 100 parts by mass on the surface of a current collector and of which thickness is 20-70 μm, and has a carbon material layer on top of the metal-contained layer, and a lithium ion secondary battery using the negative electrode is also provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a negative electrode for a lithium ion secondary battery having a high discharge capacity, and a lithium ion secondary battery.

Lithium ion secondary batteries have an excellent characteristic of high energy density compared to other secondary batteries, and are currently widely used as power sources for electronic devices. In recent years, miniaturization or performance enhancement of electronic devices has rapidly progressed, and there is an increasing demand for further higher energy density of lithium ion secondary batteries.
At present, lithium ion secondary batteries generally use LiCoO _{2 for} the positive electrode and graphite for the negative electrode. However, although the graphite negative electrode is excellent in reversibility of charge and discharge, its discharge capacity has already reached a value close to the upper limit of the theoretical value of 372 mAh / g corresponding to the intercalation compound LiC ₆ , achieving further higher energy density. In order to achieve this, it is necessary to develop a negative electrode material having a discharge capacity larger than that of graphite.

  As a negative electrode material replacing graphite, a metallic material that forms an alloy with lithium, and a composite material of the metallic material with carbon, graphite, and the like have been studied. For example, in Patent Documents 1 and 2, a first active material layer made of a metal or a semiconductor that forms an alloy with lithium is formed on a current collector, and a second active material layer made of carbonaceous material is further formed thereon. There has been proposed a negative electrode in which is formed. However, since the first active material layer covers the entire current collector and has a large expansion coefficient at the time of charging, there is a problem in that the adhesion with the current collector is reduced and the cycle characteristics are deteriorated when charging and discharging are repeated. There is.

  In Patent Document 3, a first layer mainly composed of carbon on a current collector and a second layer mainly composed of a film-like material (metal, alloy, metal oxide) having lithium ion conductivity are provided. A negative electrode formed by laminating layers has been proposed. However, since the expansion rate at the time of charging of the second layer is large, there is a problem that when the charge and discharge are repeated, the second layer is peeled off from the first layer and the cycle characteristics are deteriorated.

JP 2001-283834 A JP 2002-15729 A JP 2003-249 211 A

  The present invention has been made in view of the above situation, and is used as a negative electrode for a lithium ion secondary battery, and includes a negative electrode made of a conventional graphite material, various metal material layers, and a graphite material and / or Compared to a negative electrode composed of a laminate of a carbonaceous material composite layer, a negative electrode for a lithium ion secondary battery having a high discharge capacity, excellent cycle characteristics and initial charge / discharge efficiency, and a negative electrode for the secondary battery It is an object to provide a lithium ion secondary battery that exhibits the above characteristics.

  In the present invention, a metal-containing layer having a thickness of 20 to 70 μm containing a carbon material and 1 to 100 parts by mass of lithium and an alloyable metal with respect to 100 parts by mass of the carbon material is provided on the surface of the current collector. And a negative electrode for a lithium ion secondary battery, comprising a carbon material layer on the metal-containing layer.

  In the negative electrode for a lithium ion secondary battery of the present invention, the carbon material layer preferably has a thickness of 5 to 40 μm.

  In the negative electrode for a lithium ion secondary battery of the present invention, the metal that can be alloyed with lithium is preferably silicon and / or tin.

  In the negative electrode for a lithium ion secondary battery of the present invention, the carbon material of the metal-containing layer preferably contains natural graphite.

  In the negative electrode for a lithium ion secondary battery of the present invention, it is preferable that the carbon material layer contains a graphitized mesophase spherule.

  Moreover, the present invention is a lithium ion secondary battery using any one of the negative electrodes for lithium ion secondary batteries.

  The lithium ion secondary battery of the present invention has a metal-containing layer containing a metal that can be alloyed with a carbon material on the surface of the current collector, and has a carbon material layer on the metal-containing layer. Even if the metal is pulverized by expansion / contraction associated with charge / discharge, the metal does not peel from the metal-containing layer. In addition, since the metal-containing layer contains a carbon material that has a lower expansion coefficient than the metal and has good adhesion to the current collector, The adhesiveness is not lowered, and the conductivity can be maintained. As a result, the lithium ion secondary battery produced using the negative electrode for lithium ion secondary batteries of the present invention has high discharge capacity and initial charge / discharge efficiency, and has excellent cycle characteristics.

The present invention is described in further detail below.
(Lithium ion secondary battery)
A lithium ion secondary battery (also simply referred to as a secondary battery) usually includes a negative electrode, a positive electrode, and a nonaqueous electrolyte as main components, and these components are enclosed in, for example, a battery can. The negative electrode and the positive electrode each act as a lithium ion carrier. It is based on a battery mechanism in which lithium ions are occluded in the negative electrode during charging, and lithium ions are desorbed from the negative electrode during discharging. The lithium ion secondary battery of the present invention is not particularly limited except that the negative electrode of the present invention is used, and other constituent elements conform to the elements of a general lithium ion secondary battery.

(Negative electrode)
The negative electrode for a lithium ion secondary battery of the present invention has a structure having a metal-containing layer on the surface of a current collector and a carbon material layer on the metal-containing layer.

(Current collector)
The material of the current collector used for the negative electrode is a metal such as copper, stainless steel, nickel, or iron, and copper is particularly preferable. The shape of the current collector is not particularly limited, but a foil or a net-like material such as a mesh or expanded metal is used. In the case of a foil, the thickness of the current collector is preferably 2 to 50 μm, particularly preferably 5 to 20 μm. The size of the current collector is determined by the size of the lithium ion secondary battery.

(Metal-containing layer)
The metal-containing layer contains a carbon material and a metal that can be alloyed with 1 to 100 parts by mass of lithium with respect to 100 parts by mass of the carbon material. If the amount of metal that can be alloyed with lithium contained in the metal-containing layer is less than 1 part by mass, the effect of improving the discharge capacity of the secondary battery is small, and conversely if it exceeds 100 parts by mass, The volume expansion increases, and the cycle characteristics of the secondary battery deteriorate. The content of the metal that can be alloyed with lithium is preferably 3 to 80 parts by mass, and more preferably 5 to 60 parts by mass with respect to 100 parts by mass of the carbon material. The metal content of the metal-containing layer can be determined by a ZAF quantitative analysis method after identifying an element present from a characteristic X-ray spectrum using EPMA (electron probe microanalyzer). The thickness of the metal-containing layer is 20 to 70 μm. Preferably it is 30-50 micrometers. When the thickness of the metal-containing layer is less than 20 μm, the effect of improving the discharge capacity is small, and when it exceeds 70 μm, the internal resistance of the negative electrode is increased and the cycle characteristics of the secondary battery are deteriorated.

(Metal that can be alloyed with lithium)
A negative electrode containing a metal that can be alloyed with lithium and a carbon material in a metal-containing layer can provide a secondary battery having a higher discharge capacity than a negative electrode made of graphite not containing the metal. Metals that can be alloyed with lithium include Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, Sb, Ge, Ni, and the like. In the present invention, Si and / or Sn, which have a particularly high discharge capacity and are easily available, are preferred, and Si is most preferred. The metal may be crystalline or amorphous. Two or more alloys of the metals may be used. The metal or the alloy may further contain other elements, or a part thereof may form an oxide, a nitride, or a carbide. Although the average particle diameter of this metal should just be in the range of the thickness of a metal containing layer, Preferably it is 10 micrometers or less, More preferably, it is 0.1-5 micrometers. If the average particle diameter is more than 10 μm, the effect of improving the cycle characteristics of the secondary battery may be small. The average particle diameter means a particle diameter at which the cumulative frequency measured with a laser diffraction particle size meter is 50% by volume. The shape of the metal is not particularly limited, but is preferably granular, spherical, plate-like, scale-like, needle-like, or thread-like.

(Carbon material)
By mix | blending a carbon material with a metal content layer, the said metal can be hold | maintained at a metal content layer, maintaining electroconductivity. In the case where the metal-containing layer does not contain a carbon material and is a metal-containing layer made of only metal, conductivity cannot be ensured, and initial charge / discharge efficiency and cycle characteristics deteriorate.
The carbon material is a carbonaceous material and / or a graphite material, and has conductivity. A part of the carbon material only needs to be in contact with the metal and ensure conductivity, and the shape may be any of spherical, lump, plate, scale, and fiber.

  The carbonaceous material can be obtained by heat-treating the precursor at a temperature of 600 ° C., preferably 800 ° C. or higher. Although the kind of precursor is not ask | required, it is preferable that they are tar pitches and / or resin. Specifically, coal tar, tar light oil, tar medium oil, tar heavy oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, oxygen-crosslinked petroleum pitch, heavy oil as petroleum or coal-based tar pitches Etc. Examples of the resins include thermoplastic resins such as polyvinyl alcohol, and thermosetting resins such as phenol resins and furan resins. Preferred precursors are coal tar pitch, phenol resin and the like.

  A graphite material can also be used as the carbon material. Part or all of which is composed of a graphite material, for example, natural graphite or artificial graphite obtained by finally heat treating tar pitches at a temperature of 1500 ° C. or higher. Specifically, mesophase fired bodies, mesophase spherules and cokes obtained by heat-treating and polycondensing petroleum-based and coal-based tar pitches called graphitizable carbon materials are 1500 ° C. or higher, preferably 2000-3300. It can be obtained by graphitization at a temperature of ° C. For example, the mesophase spherulitic graphite is obtained by removing from the pitch matrix the optically anisotropic spherules that form in the pitch when coal-based or petroleum pitches are heat-treated at a temperature of 350 to 450 ° C. It is manufactured by heat treatment at a temperature of 350 to 600 ° C. under the flow of an active atmosphere, and finally heat treatment at a temperature of 1500 ° C. or higher, preferably 2000 to 3200 ° C. The graphite material may be a graphite material that has been subjected to various chemical treatments in the liquid phase, gas phase, and solid phase, heat treatment, oxidation treatment, physical treatment, and the like.

  It is also possible to use a graphitized material and a carbonaceous material in combination as the carbon material. For example, by coating scaly natural graphite, which is a graphite material, with a carbonaceous material, the initial charge / discharge efficiency can be improved when used in either a metal-containing layer or a carbon material layer. In this case, although there is no restriction | limiting in particular in both ratio, It is preferable that a carbonaceous material is 3 mass parts or more with respect to 100 mass parts of graphitized materials. If it is less than 3 parts by mass, for example, the coating on natural graphite may be incomplete.

(Carbon material layer)
The carbon material layer is a layer that contains a carbon material as a main component and does not contain a metal that can be alloyed with lithium contained in the metal content and other metals. The carbon material layer does not decrease the adhesion of the metal-containing layer to the current collector, can maintain conductivity, has a high discharge capacity and high initial charge / discharge efficiency, and provides a lithium ion secondary battery with excellent cycle characteristics. It is done. For example, when charging and discharging are repeated on a negative electrode that has only a metal-containing layer and does not have a carbon material layer, the layer structure of the metal-containing layer is destroyed by the volume expansion of the metal, and the metal-containing layer current collector Decrease in adhesion and peeling of metal occur.
The thickness of the carbon material layer is preferably 5 to 40 μm, and more preferably 10 to 30 μm. If the thickness of the carbon material layer is less than 5 μm, the initial charge / discharge efficiency may be reduced, and if it exceeds 40 μm, the internal resistance of the negative electrode may increase and the cycle characteristics of the secondary battery may be reduced. As the carbon material used for the carbon material layer, a carbon material (carbonaceous material and / or graphitic material) used for the metal-containing layer can be used. The average particle diameter of the carbon material used for the carbon material layer is preferably 1 to 30 μm, particularly preferably 5 to 15 μm. If the average particle size is less than 1 μm, the specific surface area is large, and the initial charge / discharge efficiency may be reduced. Moreover, when it exceeds 30 micrometers, when preparing a negative mix paste, carbon material particle | grains may settle, and there exists a possibility that the negative mix paste of a uniform density | concentration may not be obtained.

  The carbon material of the metal-containing layer and the carbon material of the carbon material layer may be the same or different, but the effect of improving the initial charge / discharge efficiency is greater when the carbon material layer contains a graphite material. Therefore, it is preferable. In particular, it is preferable that the carbon material layer contains graphitized mesophase spherules because the initial charge and discharge efficiency is further improved. In addition, it is preferable that the carbon material of the metal-containing layer contains natural graphite because the metal is easily retained.

(Production method of negative electrode)
The negative electrode for a lithium ion secondary battery of the present invention is formed on a metal-containing layer after forming a metal-containing layer containing a carbon material and a metal that can be alloyed with lithium on one or both surfaces of the current collector. It is produced by forming a carbon material layer.
The metal-containing layer and the carbon material layer of the negative electrode for a lithium ion secondary battery of the present invention are not limited in any way as long as the method can obtain a chemically and electrochemically stable negative electrode. Produced according to the production method. A method of using a negative electrode mixture prepared in advance by adding a binder to the negative electrode material (carbon material, metal, etc.) is preferred. As the binder, those having chemical stability and electrochemical stability with respect to the electrolyte are preferably used. For example, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol, For example, carboxymethylcellulose is used. These can also be used together.
In general, the binder is preferably used in an amount of about 1 to 20% by mass in the total amount of the negative electrode mixture.

More specifically, the negative electrode is produced as follows. First, the negative electrode material is adjusted to a desired particle size by classification or the like, and a mixture obtained by mixing this with a binder is dispersed in a solvent to prepare a negative electrode mixture in the form of a paste. That is, the slurry obtained by mixing the negative electrode material and the binder with a solvent such as water, isopropyl alcohol, N-methylpyrrolidone, dimethylformamide, and the like is stirred and mixed using a known stirrer, mixer, kneader, kneader, or the like. Then, a negative electrode mixture paste is prepared.
In order to form the metal-containing layer, it is preferable to use a negative electrode material obtained by mixing a carbon material and a metal at a predetermined ratio, for example, the negative electrode mixture paste. In this case, heat treatment may be performed after mixing the carbon material and the metal. The heating temperature is not particularly limited, but is preferably performed at a temperature lower than the temperature at which the metal reacts with the carbon material. For example, in the case of Si, at a temperature of 1500 ° C. or higher, it reacts with carbon to produce SiC that does not have charge / discharge capability, so the heat treatment temperature is preferably less than 1500 ° C., and preferably 900 to 1200 ° C. Particularly preferred.

  A negative electrode mixture layer can be formed by applying the paste to one or both sides of a current collector and drying. After forming the negative electrode mixture layer, pressurization such as pressing may be performed. The metal-containing layer is a negative electrode mixture layer containing a metal, and the carbon material layer is a negative electrode mixture layer containing no metal and is adjusted to have the thickness described above. In addition, as the negative electrode for a lithium ion secondary battery of the present invention, a material obtained by dry-mixing a powder of polyethylene, polyvinyl alcohol or the like into the above-described negative electrode material and hot pressing it can be used.

(Positive electrode)
The positive electrode is formed, for example, by applying a positive electrode mixture composed of a positive electrode material, a binder and a conductive agent to the surface of the current collector. As a positive electrode material (positive electrode active material) used in the lithium ion secondary battery of the present invention, a lithium compound is used, and it is preferable that it can absorb and desorb a sufficient amount of lithium. Such lithium compounds include lithium-containing transition metal oxides, transition metal chalcogenides, lithium-containing compounds such as vanadium oxides and lithium compounds thereof, general formula M _x Mo ₆ S _8-Y (where M is a transition metal, etc.) X is a number satisfying 0 ≦ X ≦ 4, and Y is a number satisfying 0 ≦ Y ≦ 1), activated carbon, activated carbon fiber, and the like. Examples of the vanadium oxide include those represented by V ₂ O ₅ , V ₆ O ₁₃ , V ₂ O ₄ , and V ₃ O ₈ .

The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a composite oxide in which lithium and two or more transition metals are dissolved. The composite oxide may be used alone or in combination of two or more. Specifically, the lithium-containing transition metal oxide is LiM ¹ _1-z M ² _z O ₂ (wherein M ¹ and M ² are at least one transition metal, and Z is a number of 0 ≦ Z ≦ 1). Or LiM ¹ _2-w M ² _w O ₄ (wherein M ¹ and M ² are at least one transition metal, and W is a number of 0 ≦ W ≦ 2). In the formula, transition metals represented by M ¹ and M ² are Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn and the like, and preferred specific examples are LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _0.9 Co _0.1 O ₂ , LiNi _0.5 Mn _0.5 O ₂ and the like.
The lithium-containing transition metal oxide is, for example, lithium, a transition metal oxide, salt or hydroxide as a starting material, and these starting materials are mixed according to the composition of the desired metal oxide, and an oxygen-containing atmosphere It can be obtained by firing at a temperature of 600 to 1000 ° C. below.

In the lithium ion secondary battery of the present invention, the positive electrode active material may be used alone or in combination of two or more. Moreover, carbonates, such as lithium carbonate, can also be added in a positive electrode. Moreover, when forming a positive electrode, conventionally well-known various additives, such as a electrically conductive agent and a binder, can be used suitably. As the conductive agent, known materials such as graphite and carbon black can be used.
Similarly to the negative electrode, the positive electrode is made into a positive electrode mixture paste by dispersing the positive electrode mixture in a solvent, and this positive electrode mixture paste is applied to a current collector and dried to form a positive electrode mixture layer. Alternatively, after forming the positive electrode mixture layer, pressurization such as pressing may be further performed. Thereby, the positive electrode mixture layer is uniformly and firmly bonded to the current collector.
The shape of the current collector is not particularly limited, and a foil shape or a net shape such as a mesh or an expandable metal is used. Examples of the material of the current collector include aluminum foil, stainless steel foil, and nickel foil. The thickness is preferably 10 to 40 μm.

(Nonaqueous electrolyte)
As the nonaqueous electrolyte used in the lithium ion secondary battery of the present invention, an electrolyte salt used in a normal nonaqueous electrolyte solution can be used. Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ), LiCl, LiBr, LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ CH ₂ OSO ₂ ) ₂ , LiN (CF ₃ CF ₃ OSO ₂ ) ₂ , LiN (HCF ₂ CF ₂ CH ₂ OSO ₂ ) ₂ , LiN {(CF ₃ ) Lithium salts such as ₂ CHOSO ₂ } ₂ , LiB {(C ₆ H ₃ (CF ₃ ) ₂ } ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ are used. In particular, LiPF ₆ and LiBF ₄ are preferred from the viewpoint of oxidation stability, and the electrolyte salt concentration in the electrolyte solution is preferably 0.1 to 5 mol / l, preferably 0.5 to 3.0 mol / l. More preferred .

  Solvents for preparing the electrolyte solution include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyl Tetrahydrofuran, γ-butyrolactone, 1,3-dioxofuran, 4-methyl-1,3-dioxolane, ethers such as anisole and diethyl ether, thioethers such as sulfolane and methylsulfolane, nitriles such as acetonitrile, chloronitrile and propionitrile, boron Trimethyl acid, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene, benzoyl chloride, bromide Nzoiru, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazoline, ethylene glycol, may be used an aprotic organic solvent such as dimethyl sulfite.

  When the nonaqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte, a polymer gelled with a plasticizer (nonaqueous electrolyte solution) is used as a matrix. Examples of the polymer compound constituting the matrix include ether polymer compounds such as polyethylene oxide and cross-linked products thereof, methacrylate polymer compounds such as polymethacrylate, acrylate polymer compounds such as polyacrylate, polyvinylidene fluoride ( Fluorine polymer compounds such as PVDF) and vinylidene fluoride-hexafluoropropylene copolymers are preferred. These can also be mixed and used. From the viewpoint of oxidation-reduction stability, a fluorine-based polymer compound such as PVDF or vinylidene fluoride-hexafluoropropylene copolymer is particularly preferable.

  A plasticizer is blended in the polymer solid electrolyte or the polymer gel electrolyte. As the plasticizer, the electrolyte salt and the non-aqueous solvent can be used. In the case of a polymer gel electrolyte, the concentration of the electrolyte salt as a plasticizer in the nonaqueous electrolyte solution is preferably 0.1 to 5 mol / l, more preferably 0.5 to 2.0 mol / l. .

The method for producing such a solid electrolyte is not particularly limited. For example, a method of mixing a polymer compound constituting a matrix, a lithium salt, and a nonaqueous solvent and heating to melt and dissolve the polymer compound, an organic solvent A method of dissolving an organic solvent after dissolving a polymer compound, a lithium salt, and a non-aqueous solvent, and a mixture of a polymerizable monomer, a lithium salt, and a non-aqueous solvent as a raw material of the polymer electrolyte, and mixing the mixture with ultraviolet rays, electrons Examples thereof include a method of producing a polymer electrolyte by polymerizing by irradiating a beam or a molecular beam.
Moreover, 10 to 90 mass% is preferable and, as for the addition rate of the nonaqueous solvent in the said solid electrolyte, 30 to 80 mass% is more preferable. If it is less than 10% by mass, the electrical conductivity will be low, and if it exceeds 90% by mass, the mechanical strength will be weak and film formation will be difficult.

(Separator)
In the lithium ion secondary battery of the present invention, a separator can be used. Although the material of a separator is not specifically limited, A woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are illustrated. A synthetic resin microporous membrane is preferred, and among these, a polyolefin-based microporous membrane is preferred from the standpoints of film thickness, membrane strength, membrane resistance, and the like. Specifically, it is a microporous film made of polyethylene and polypropylene, or a microporous film in which these are combined.

In the lithium ion secondary battery of the present invention, a gel electrolyte can be used because of high initial charge / discharge efficiency.
The gel electrolyte secondary battery is configured by laminating a negative electrode, a positive electrode, and a gel electrolyte in the order of, for example, a negative electrode, a gel electrolyte, and a positive electrode, and accommodating the stacked layers in a battery exterior material. Further, a gel electrolyte may be disposed outside the negative electrode and the positive electrode. In particular, in a secondary battery using a gel electrolyte for the negative electrode of the present invention, the gel electrolyte can contain propylene carbonate. In general, propylene carbonate has a strong electrolysis reaction with respect to graphite. However, since the decomposition reactivity with the negative electrode of the present invention is low, the irreversible capacity in the first cycle can be kept small.

  Furthermore, the structure of the lithium ion secondary battery of the present invention is not particularly limited, and is not particularly limited with respect to its shape and form, depending on the application, mounted equipment, required charge / discharge capacity, etc., cylindrical type, Any shape or form of a square shape, a coin shape, or a button shape may be used. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to provide means for detecting an increase in the internal pressure of the battery and shutting off the current when an abnormality such as overcharge occurs. In the case of a polymer solid electrolyte battery or a polymer gel electrolyte battery, a structure enclosed in a laminate film can also be used.

Moreover, this invention is also a lithium ion secondary battery formed using the said negative electrode for lithium ion secondary batteries.
The lithium ion secondary battery of the present invention is not particularly limited except that the negative electrode is used, and other battery components are configured as described above according to the elements of a general lithium ion secondary battery, Produced.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In Examples and Comparative Examples, an evaluation button type secondary battery having a configuration as shown in FIG. 1 was produced and evaluated. A real battery can be manufactured according to a well-known method based on the objective of this invention.
The average particle size was a particle size at which the cumulative frequency of the particle size distribution measured with a laser diffraction particle size distribution meter was 50% by volume as described above. Further, the residual carbon ratio is based on the fixed carbon method of JIS K2425-1983, and the coal tar pitch is heated to a temperature of 800 ° C., which means the residual when the entire amount is carbonized, expressed as a percentage. Is.

Example 1
(Production of working electrode)
Coal tar pitch (manufactured by JFE Chemical Co., Ltd., PK-QL, residual carbon ratio 60 mass%) was mixed with tar oil (solvent) to obtain a coal tar pitch solution. Next, Si powder (manufactured by High Purity Chemical Laboratory Co., Ltd., average particle size 2 μm) and natural graphite [manufactured by Chuetsu Graphite Industries, Ltd., average particle size 10 μm] are added to the coal tar pitch solution at 200 ° C. Kneaded for 1 hour. At that time, the solid content mass ratio was adjusted to be Si: natural graphite: coal tar pitch = 10: 70: 33.3. After kneading, the oil in tar was removed from the kneaded product by vacuum. The obtained kneaded product was coarsely pulverized and then fired at 1000 ° C. for 10 hours to obtain a composite composed of a carbonaceous material containing substantially no volatile matter. The average particle diameter of the composite was 15 μm, and Si: carbon material of the composite (natural graphite + carbon material of coal tar pitch) = 10: (70 + 20) = 11: 100. 90 parts by mass of the composite and 10 parts by mass of a polyvinylidene fluoride binder are placed in an N-methylpyrrolidone solvent and stirred and mixed at 2000 rpm for 30 minutes using a homomixer to prepare an organic solvent-based negative electrode mixture paste A. did.

  Mesophase microspheres (manufactured by JFE Chemical Co., Ltd., KMFC) were heated to 3000 ° C. and graphitized, and then the powder was classified and the particle size was adjusted to obtain a graphite particle powder having an average particle size of 18 μm. 90 parts by mass of the graphitic particle powder and 10 parts by mass of the binder polyvinylidene fluoride are placed in an N-methylpyrrolidone solvent, and are stirred and mixed at 2000 rpm for 30 minutes using a homomixer to prepare an organic solvent-based negative electrode mixture paste B. Was prepared.

  Paste A was applied on a current collector copper foil (thickness: 16 μm), and paste B was further applied thereon. Then, the solvent was volatilized and dried at 90 ° C. in vacuum, and the negative electrode mixture layer was pressurized by a hand press to form a metal-containing layer and a carbon material layer on the metal-containing layer. This was punched into a cylindrical shape with a diameter of 15.5 mm to produce a working electrode held by the current collector. The content ratio of the metal that can be alloyed with lithium was determined by the ZAF quantitative analysis method using EPMA for the cross section of each layer after pressing (1000 times magnification). As for the cross section, 10 visual fields were observed, and the average value was adopted. Moreover, the thickness of each layer was taken as the average value of 10 places measured with SEM (scanning electron microscope). The results are shown in Table 1.

(Production of counter electrode)
The lithium metal foil was pressed against a nickel net and punched into a circular shape with a diameter of 15.5 mm to produce a counter electrode made of a lithium metal foil in close contact with a current collector made of nickel net.

(Electrolyte, separator)
LiPF ₆ was dissolved at a concentration of 1 mol / l in a mixed solvent obtained by mixing 33 vol% ethylene carbonate and 67 vol% methyl ethyl carbonate to prepare a nonaqueous electrolytic solution. The obtained non-aqueous electrolytic solution was impregnated into a polypropylene porous body (thickness 20 μm) to produce a separator impregnated with the electrolytic solution.

(Evaluation battery)
A button-type secondary battery shown in FIG. 1 was produced as an evaluation battery.
The working electrode 2 in close contact with the current collector 7b and the counter electrode 4 in close contact with the current collector 7a were laminated with the separator 5 impregnated with the electrolyte interposed therebetween. Thereafter, the exterior cup 1 and the exterior can 3 were combined so that the current collector 7 b side was accommodated in the exterior cup 1 and the current collector 7 a side was accommodated in the exterior can 3. At that time, an insulating gasket 6 was interposed between the peripheral edges of the outer cup 1 and the outer can 3, and both peripheral edges were caulked and sealed.

(Charge / discharge test)
The evaluation battery was subjected to the following charge / discharge test at a temperature of 25 ° C., and the charge / discharge capacity, initial charge / discharge efficiency, and cycle characteristics were measured and calculated. The evaluation results are shown in Table 1. (Discharge capacity, initial charge / discharge efficiency)
The constant current charging was performed until the circuit voltage reached 0 mV at a current value of 0.9 mA. When the circuit voltage reached 0 mV, switching was made to constant voltage charging, and the charging was continued until the current value reached 20 μA. The charging capacity was determined from the amount of electricity applied during that time. Then, it rested for 120 minutes. Next, constant current discharge was performed until the circuit voltage reached 1.5 V at a current value of 0.9 mA, and the discharge capacity was determined from the amount of current applied during this period. This was the first cycle. The initial charge / discharge efficiency was calculated from the following equation. In this test, the process of occluding lithium ions in the graphite particles was charged and the process of detaching was defined as discharge.
Initial charge / discharge efficiency (%) = (first cycle discharge capacity / first cycle charge capacity)
× 100

An evaluation battery different from the evaluation battery that evaluated the discharge capacity and the initial charge / discharge efficiency was produced, and the following evaluation test was performed.
After 4.0 mA constant current charging was performed until the circuit voltage reached 0 mV, switching to constant voltage charging was continued until the current value reached 20 μA. The charging capacity was determined from the amount of electricity applied during that time. Then, it rested for 120 minutes. Next, constant current discharge was performed until the circuit voltage reached 1.5 V at a current value of 4.0 mA, and the discharge capacity was obtained from the energization amount during this period. This charging / discharging was repeated 20 times, and the cycle characteristics were calculated from the obtained discharge capacity using the following equation.
Cycle characteristics (%) = (discharge capacity of 20th cycle / discharge capacity of 1st cycle)
× 100

(Comparative Example 1)
In Example 1, as shown in Table 2, a negative electrode and an evaluation battery were produced under the same method and conditions as in Example 1 except that the application order of paste A and paste B was changed. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 2.

(Comparative Example 2)
In Example 1, as shown in Table 2, the paste A was applied to a copper foil to form a first layer whose thickness was changed from 40 μm to 50 μm, and sputtering was performed on the layer using silicon as a target. A negative electrode and an evaluation battery were prepared in the same manner and under the same conditions as in Example 1 except that a silicon thin film (thickness 5 μm) was formed as the second layer. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 2.
In the sputtering, an electrode coated with paste A is disposed on the anode side stage of a DC bipolar sputtering apparatus, a single crystal silicone target having a purity of 99.999% is disposed on the cathode, an argon atmosphere, a pressure of 0.5 Pa, The test was performed for 2 hours under conditions of a voltage of 600 V and a current of 0.5 A.

(Comparative Example 3)
In Example 1, as shown in Table 2, sputtering was performed on a copper foil using silicon as a target, a silicon thin film (thickness 5 μm) was formed as a first layer, paste A was applied on the thin film, A negative electrode and an evaluation battery were produced in the same manner and under the same conditions as in Example 1 except that the second layer was changed from 40 μm to 50 μm and the third layer was formed by applying paste B. . The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 2.
In the sputtering, a copper foil is disposed on the anode side stage of a DC bipolar sputtering apparatus, a single crystal silicone target having a purity of 99.999% is disposed on the cathode, a pressure of 0.5 Pa, a voltage of 600 V, and a current in an argon atmosphere. This was carried out for 2 hours under the condition of 0.5 A.

(Examples 2-3)
In Example 1, except that the content of silicon powder in the metal-containing layer was changed as shown in Table 1, a negative electrode mixture paste was prepared by the same method and conditions as in Example 1, and the negative electrode and the evaluation battery were prepared. Produced. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 1.

(Comparative Example 4)
In Example 1, except that the content of the silicon powder in the metal-containing layer was changed as shown in Table 2, a negative electrode mixture paste was prepared by the same method and conditions as in Example 1, and the negative electrode and the evaluation battery were prepared. Produced. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 2.

(Examples 4 to 6)
In Example 1, except that the thickness of the metal-containing layer was changed as shown in Table 1, a negative electrode mixture paste was prepared by the same method and conditions as in Example 1, and a negative electrode and an evaluation battery were produced. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 1.

(Comparative Example 5)
In Example 1, except that the thickness of the metal-containing layer was changed as shown in Table 2, a negative electrode mixture paste was prepared by the same method and conditions as in Example 1, and a negative electrode and an evaluation battery were produced. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 2.

(Examples 7 to 10)
In Example 1, except that the thickness of the carbon material layer was changed as shown in Table 1, a negative electrode mixture paste was prepared by the same method and conditions as in Example 1, and a negative electrode and an evaluation battery were produced. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 1.

(Examples 11 to 12)
In Example 1, except that the content of Si was changed as shown in Table 1, a negative electrode mixture paste was prepared by the same method and conditions as in Example 1, and a negative electrode and an evaluation battery were produced. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 1.

(Example 13)
In Example 1, except that the carbon material of the carbon material layer was changed to natural graphite, a negative electrode mixture paste was prepared by the same method and conditions as in Example 1, and a negative electrode and an evaluation battery were produced. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 1.

(Examples 14 to 15)
In Example 1, during the production of the carbon material of the metal-containing layer, the coal tar pitch was changed to a phenol resin [Showa Polymer Co., Ltd., “APH-N3001”] or a furan resin [manufactured by Lignite Co., Ltd.]. Is changed to ethanol and silicon powder to tin powder [Aldrici Co., Ltd., average particle size of 10 μm or less], and the amount of tin powder to 100 parts by mass of the carbon material is changed to 18 parts by mass, A negative electrode mixture paste was prepared by the same method and conditions as in Example 1, and a negative electrode and an evaluation battery were produced. The evaluation battery was subjected to a charge / discharge test in the same manner as in Example 1 to determine the discharge capacity, initial charge / discharge efficiency, and cycle characteristics. The evaluation results are shown in Table 1.

  The evaluation batteries of Examples 1 to 15 have a metal-containing layer containing a carbon material and a metal that can be alloyed with lithium on the surface of the current collector, and a negative electrode having a carbon material layer on the metal-containing layer Therefore, a negative electrode (Comparative Example 1) provided with a layer made of a metal and graphite on a graphite layer, a negative electrode (Comparative Example 2) provided with a metal layer on a layer made of metal and graphite, A negative electrode (Comparative Example 3) provided with a layer comprising a metal and graphite, and a carbon material layer, a negative electrode with a high metal content in the metal-containing layer (Comparative Example 4), and a negative electrode with a thick metal-containing layer (Comparative) It can be seen that the initial charge and discharge efficiency is high and the cycle characteristics are excellent while maintaining a high discharge capacity as compared with Example 5). Moreover, the evaluation battery of Examples 7-10 has shown that there exists a suitable range in the thickness of a carbon material layer.

It is a schematic cross section which shows the structure of the button type evaluation battery for using for a charging / discharging test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior cup 2 Working electrode 3 Exterior can 4 Counter electrode 5 Separator 6 Insulating gasket 7a, 7b Current collector

Claims (6)

  The surface of the current collector has a metal-containing layer having a thickness of 20 to 70 μm containing a carbon material and 1 to 100 parts by mass of lithium and an alloyable metal with respect to 100 parts by mass of the carbon material, A negative electrode for a lithium ion secondary battery, comprising a carbon material layer on a metal-containing layer.   The negative electrode for a lithium ion secondary battery according to claim 1, wherein the carbon material layer has a thickness of 5 to 40 μm.   The negative electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the metal that can be alloyed with lithium is silicon and / or tin.   The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the carbon material of the metal-containing layer contains natural graphite.   The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the carbon material layer contains graphitized mesophase spherules.   A lithium ion secondary battery using the negative electrode for a lithium ion secondary battery according to any one of claims 1 to 5.

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